Process for the manufacture of organic acid anhydrides



Jan. 16, 1945. n. c. HULL EIAL 1 2,367,501

PROCESS FOR THE MANUFACTURE OF ORGANIC ACID ANHYDRIDES Original Filed May 18, 1939 2 Sheets-Sheet 1 w H OOUT E FIIGJ.

BR/Nf 9 our VACUUM 6 COLUMN WEAK ACID m ('ONDENSEi J0 BR/NE IN ll HEAT REDUCED IN 1 n- CATALYST J R OUT RETURN T0 OXIDATION UNIT I Z4\ 18: 1 "299% 1 l 1 I I I mmzrsrsozunonmrwFFor V OJIDAT/ON AIR NIT Rz'm/amA/vr l I DRYING TUBE- ALDEHYDL' I FEED 12 2s ACETIC v ANHWRIDE WfA/(fl MET/c DIFFUSION m1:

ACID 04mm PUMP David C. Hull Clazr A.Marshall INVENTORS yam-10% AT! RNl ZYS Jane 16, 1945. Y D. c. HULL EEAL I ZSG'ZQSM PROCESS FOR THE MANUFACTURE OF ORGANIC ACiD ANHYDRIDES Original Filed May 18, 1939 DEPHLEQMATOR 2 A 63 2 Sheets-Sheet 2 6145.70 .SCRUBBER FOR COMPLETE REMOVAL OF ALDEHYDE AND ACID I 52 gggg gf -c0 DEN5ER VENT ACID AND v I CONDENSER 5 AANYDR/DE 5EPARAT0R t VACUUM 46 44 STILL l J 1 METER 5 E 6i 62 H 47 57 L fifth fAc/D AND OXIDATION BASE F v ANHYDR/DE UNIT\-\ HEATER F fmqr g 56 J] AND Ac/D 57/? NON-CONDf/V5AB1E5 POT T0 COOLER 0R SCRUBBER FOR REMOVAL or ALDEHYDE CIRCULATED c'ATALYsT 4] LIOUORSIF/PPL'D orl-l o 7 r f wcuuM ALDEAYDE EEED LA/R IN /55 P 66 OR MIXED FEED 1 OEALDEHYDE Z AND AcET/cAc/D o l l IANNYD IDE ANDAc/D PUMP' T0 BEC'ONCENTRATED I l BY DISTILLATION 2?":22535? TO BE CONCENTRATED David C. Hull AZFOTROPIGJLLY ClalrAMarshall INVENTORS JBY Z 7h 0 A Awgmsys Patented Jan. 16, 1945 PROCESS FOR THE MANUFACTURE OF ORGANIC ACID ANHYDRIDES David 0. Hull and Claire A. Marshall, Kingsport, Tenn., assignors to Eastman Kodak. Company, Rochester, N. Y., a corporation of New Jersey Original application May 18, 1939, Serial No.

274,426. Divided and this application September 26, 1940, Serial No. 358,532

This invention relates to the manufacture of 3 Claims.

anhydrides of aliphatic acids and more particularly to process and catalyst for the manufacture of acetic anhydride and other lower aliphatic anhydrides.

This application is a division of our copending U. S. application 274,426, Patent No. 2,283,209, which is a continuation-in-part of our copend- 1 ing application S. N. 139,522.

conversion of acetone and the like into anhydrides. It has also been suggested that aldelwdes may be directly oxidized to anhydrides in accordance with the equation In this type of process large amounts of aldehyde as, for example, 1200 parts of aldehyde containing catalyst, have been placed in an oxidation unit and oxidized under pressure, then cooled to a C. Chemicals have been added to the reaction mixtures for taking up water or anhydride.

However, such latter type processes possess disadvantages and dangers. As can readily be appreciated, by having all of the aldehyde present in the unit at one time there would be considerable danger of explosion. The step of mixing other chemicals with the anhydride for the purpose of removing water not only involves the expense and trouble of adding a foreign material to the reaction mixture, but also presents the possibility of contaminating the anhydride- We have found a greatly improved procedure for manufacturing anhydrides which is more direct than the first mentioned prior art type of process and represents a new and superior process over other processes which have been suggested, in that it is not only efilcient but less dangerous-and permits the production of a high grade anhydride uncontaminated by foreign components.

This invention has for one objectto provide a process for the manufacture of aliphatic acid anhydrides which is substantially continuous and direct. Still another object is to provide an oxidation process for the production of anhydrides of the lower aliphatic acids. A still further object is to provide a catalytic oxidation process together with a process of recovery for the production of organic acid anhydrides. Another object is to provide a process for converting aldehydes substantially directly to organic acid anhydrides. Still another object is to provide a continuous procedure in the production of organic acid anhydrides by oxidation in catalyst. solutions, whereby the anhydrides may be readily and efficiently separated.

Still another object is to provide a novel catalyst solution that is particularly useful for the treatment of aliphatic aldehydes. Still another object is to provide a catalyst solution essentially comprising salts of eighth group metals from the periodic system, which solution may be employed in various ways without the generation of dangerous quantities of peracetic acid. Still another object is to provide a catalyst solution which exerts a minimum of decomposition reaction on lower aliphatic acid anhydrides.

Still another object is to provide a novel meth- 0d of manufacturing catalyst solution containing nickel salts and cobalt salts. A still further object is to provide a process of treating catalyst solutions containing nickel salts and cobalt salts to increase their activity. Other objects will appear hereinafter.

For a more complete understanding of our invention reference is made to the attached drawings.

Fig. 1 is a semi-diagrammatic side elevation view in the nature of a flow sheet showing one type of apparatus arrangement which may be employed for carrying out our process.

Fig. 2 is another side elevation view of 9. diagrammatic lay-out of apparatus for carrying out a modified type of process.

In Fig. 1, the numeral indicates a feed con-- perature therein. The upper portion of the column may be provided with temperature control-= ling unit designated l8. The upper portion of the unit is connected through the conduit I! to separator l. Separator l is provided with a.

condenser conduit means 5 for separating unconsumed and uncondensible gases as'will be described hereinafter. Separator 4 is also provided with return conduit 2| to the column. The lower portion of the column 3 is provided with another feed inlet 2 for oxidizing medium. While we show a plurality of feed inlets, we also contemplate the use of a single conduit and premixing. Conduit 2 may be connected to drying apparatus l5 and a condenser l4 for the purpose of drying the oxidizing medium.

Referring again to the upper portion of the oxidation equipment, a valved conduit l6 interconnects the oxidation equipment with the flash pot 6. This flash pot may be constructed similar to any conventional still pot or base heater. The lower and intermediate sections of the flash pot are also interconnected bymeans of conduits 22, 23, 24 and 25, so as to provide return to the oxidation unit. The flash pot is also connected by means of conduit 21 to vacuum column 8. This column may be of any standard construction but preferably will be of a type which facilitates the application of reduced pressure thereto. The lower portion thereof will be provided with heating means ll and a drawoif means l2. The upper portion of the column 8 is provided with a dephlegmator or condenser means 9. The upper portion is also provided with a draw-off conduit 28 through which materials may be removed and condensed at l and further withdrawn at conduit IS. The reduced pressure producing equipment (not shown) may be attached to the unit at some point along this line.

Fig. 2 is in a number of respects similar to Fig. 1. Suitable feed conduits are provided at 4! and 42. 'Anoxidation unit of any of the aforementioned types already described, having a diffusing disk, or nipples in the base, and cooling coils within the unit, is provided at 43. The upper portion of the unit is connected to separator 44 by means of conduits 48 and 41. Means for removing gaseous components is provided at 48.

The separator 44 is connected by valved conduit 49 to a vacuum still i, packed with Raschig rings. This column is provided with dephlegmator 52 in the upper portion thereof and vapor ofi-take conduit 53, whichleads through condenser 54 as an acid-cooling means. The lower portion of still 5| is provided and interconnected with a base heater 56 and astill pct 51. These units are also connected by conduit 58 to the oxidation unit. The still .pot is connected by means of conduit 62 through a condenser 8| to anhydride and acid collecting receivers. The several parts aforementioned are interconnected by conduits 62, 63, 84 and 65 to a vacuum equipment designated 66.

In the above described apparatus lay-outs it is to be understood that suitable meters, thermometers and other control equipment may be inserted where desired. Preferably, the oxidation equipment is to be constructed of aluminum or aluminum alloys. However, other materials and alloys may be employed. If desired, the various equipment or parts thereof may be constructed of iron or various types of stainless steel.

The functioning of our novel apparatus will be apparent from the following description wherein several examples of processes which may be carried out therein are described. 7 I

After considerable investigation of oxidation procedure and related procedure, we have found that anhydride may be directly formed by oxidizing aldehydes and that the anhydrides, though reactive under normal conditions, by our novel procedure may be continuously recovered to a substantial extent and that the resulting oxidation mixture containing the desired anhydride may be substantially continuously obtained by our novel practices described herein. As indicated above, in the direct oxidation of aldehyde to obtain anhydride there is a molecule of water formed corresponding to every molecule of anhydride produced. In the direct oxidation type of processes now available this water formation would tend to dilute the catalyst and otherwise present problems. That is, in the oxidation processes described in certain foreign publicatiohs wherein all of the aldehyde is placed .in the unit at one time, there would also be formed in the unit during the operation of the process a molecule of water for each molecule of anhydride, which water would not only dilute the reaction products but would also dilute the catalyst solution. We have found these disad vantages and others may be overcome or substantially minimized. While there is a marked tendency of anhydrides to react with water and form acids, which rate of reaction is quite rapid under normal atmospheric conditions, we have found that this rate of reaction is considerably diminished under other conditions; hence, by our continuous process we are able to overcome to some extent and delay the undesired reactions of the anhydride and thereby are able to recover substantial amounts of the anhydride which we have produced.

While in the following description we have set forth teachings relative to two carbon atom-aldehydes such as acetaldehyde, it is to be understood that the process and catalyst may be employed with three and four carbon atom aldehydes such as propionic and butyric aldehydes or mixtures either gaseous or liquid, containing at least one of these aldehydes such as, for example, hydrocarbon gases containing a content of acetaldehyde.

,An oxidation unit is filled with catalyst solution. The catalyst solution may comprise a cobalt containing catalyst of the type described in U. S. Patents 1,976,756 and 1,976,757. However, we prefer to employ a catalyst solution containing certain ingredients in certain proportions. We have found that a catalyst solution for best conversion of aldehyde to anhydride should contain greater than 2% cobalt salt, as for example a quantity within the range of 2-6% cobalt salt. We have found, however, that still increased production may be obtained by including in the composition an addition of nickel salt. Too high percentages of nickel salt, however, possess certain disadvantages in causing reactions which produce loss of product and give an uneven operation. I

We have found that the nickel salt should be below about 2% and the cobalt salt about 2%. Various nickel and cobalt salts may be employed and generally a salt would be used corresponding to the compound being produced in the process employing the catalyst. That is, in a process of producing acetic anhydride a small amount of nickel acetate in acetic acid solution with, for example, 3-12% of cobaltic acetate wouldbe employed. This solution might also contain acetic anhydride. We have expressed our catalyst concentration in weight percent of the catalyst'mixture. It will be observed as the description proceeds that in our process the composition of our mixture is maintained substantially cmstant because the composition and quantity of the catalyst solution in our apparatus do not materially change, since the added ingredients and reaction products are not allowed to build up therein.

In. some instances, particularly where the catalyst solution has a low content of water (less than or is anhydrous with or without a content of anhydride, a percent up to 12% nickel salts in any combination with up-to 20% cobalt salts may be employed. I

We have found that our catalyst solution composed of the two salts in combination as described will yield as high as 45% of the aldehyde used, in the form of anhydride and yield 92%- 95% or better of anhydride plus acid with respect to the aldehyde oxidized.

We have also found that our novel catalyst comprising a certain proportion of nickel salt in solution with a certain proportion of cobalt salt functions very well at relatively low temperatures of operation, as for example, between 0 C. and 30 C. Even at these temperatures various aldehydes may be readily converted to anhydride by oxidation and the catalyst solution completely changed or circulated from the oxidation unit completely, for example, every dium in combination with a 2-5 carbon atom aliphatic aldehyde would be passed through the solution until a color change occurred. Thereafter, the nickel salt such as the acetate, oxide or the like would be added and the passage of the oxidizing medium and aldehyde continued for a short time. The catalyst may then be employed for oxidation procedure and will be found to possess a high degree of activity. In'addition, in the particular catalyst solution employed in our novel processes herein described, we also contemplate the addition of the corresponding organic acid anhydride thereto. That is, in the instance of acetaldehyde oxidation, our catalyst solution would preferably contain a content of acetic anhydride. l

The aldehyde to be oxidized may be fed in either the liquid or vapor phase through single conduits or pre-mixed with the oxidizing medium. Ifv desired, pressure can be applied to the oxidation step but we prefer to employ only about suficient pressure to overcome the hydrostatic pressure of the catalyst solution. Or, if desired, reduced pressure can be employed for assisting or overcoming the hydrostatic pressure or resistance, the catalyst solution may offer to the passage of the aldehyde therethrough. The

oxidizing medium may comprise air, ozone or solution described anhydride is formed, but as.

previously indicated, it is necessary to prevent further reaction thereof. By our apparatus aracetic anhydride, acetic acid, catalyst and some water, together with off-gases, is subjected to separation and reduced pressure. We have found this materially delays further reaction of the anhydride. The solution is then treated to remove acetic acid and water. Any acid in the anhydride may be readily separated therefrom.

A certain amount of the withdrawn acetic acid, together with some anhydride is preferably returned to'the oxidation unit for keeping the solution in the oxidation unit more or less at a constant level and of a composition that does not vary to too great an extent.

. Should iron equipment be employed and a high content of CO2 be indicated in the off-gases, thereby evidencing that a part of the materials are being over-oxidized, the addition of a phosphate, or other iron precipitant to the catalyst solution, will impart an improvement thereto.

The anhydride produced may be further concentrated and employed for any of the desired purposes such as in the manufacture of cellulose esters and the like. The organic acid produced in conjunction with the production of anhydride may be further concentrated to a completely anhydrous acid and returned to the catalyst solution or the anhydrous acid may be converted by pyrolysis to ketene or anhydrides.

A still further understanding of our process may be obtained by the consideration of the following examples which are set forth to illustrate our preferred embodiment. In consideration of the first example, reference is made to Fig. 1 of the drawings:

Example Acetaldehyde is fed in through conduit l to oxidation column 3 which contains as a catalyst either cobalt acetate alone or nickel acetatecobalt acetate in acetic acid, acetic anhydride and water as already described in detail. Through this solution a stream of air, dried by passing through cooler l4 and calcium chloride dryer i5, is passed in through conduit 2. If desired, the oxidizing medium may be compleely dried merely by the application of refrigeration thereto to cause a chilling out of moisture from the oxidizing medium, or drying means alone may be employed. The temperature of the catalyst solution is preferably maintained at 30 C.-35 C. by a stream of cooling medium as water through the jacket of 3. The nitrogen left from the oxidation process together with a slight excess of oxygen, is carried out through separator 4 to reflux condenser 5 and then to a scrubber for removal of traces of acid and aldehyde. That is, any of the aldehydes or acids which may be removed, due to entrainment in the oxidizing medium are preferably removed by some suitable treatment. As the liquid formed in the oxidation process buildsup in separator d it is drawn up by vacuum to flash pot 6. A portion is here flashed off to vacuum column 8. The excess liquid overflows from 5 through conduits 22, 23,-

solution every few minutes keeps the catalyst solution in its highest state of efllciency, since undesired constituents as water are eliminated, it is possible to change the catalyst solution at greater intervals as, for example, every several hours. In general, we would always completely change the catalyst solution once in every twentyfour hours. Inasmuch as our catalyst solution is substantially continuously conducted to a heating unit wherein the water, aqueous acetic acid and other constitutents which would decompose the anhydride formed are eliminated and the improved catalyst solution returned to the oxidation unit, it is apparentthat our catalyst solution may be substantially continuously maintained in a high state of efllciency. A meter can be used in the line from 4 to 6 to control this flow. The amount of vapors flashed from 6 to vacuum still 8 is such that the level in 4 remains substantially constant; the vapors consist of acid, water and anhydride. Here the water is removed through dephlegmator 9 to condenser l along with a quantity of acid, this water-acid mixture is drawn off through a barometric leg [3 overflowing from a sealed vessel as shown. From the base of still 8 through base heater II, which supplies the heat necessary for the distillation, the mixture of acid and anhydride overflows through a barometric leg l2 and overflows from a sealed vessel as shown. Oxidation column 3 can be operated at either increase, normal or reduced pressures.

For example, a total of 37 lb. of acetaldehyde were fed into oxidation column 3, which was maintained at 30 C.35 ,0. During this time 24.5 lb. of 30% acetic anhydride were collected from overflow l2, and 11 lb. of 86% acetic acid (2% aldehyde and 12% water) were removed from overflow 13, while the scrubber water from the nitrogen scrubber and discharge from the vacuum pumps contained an additional 2.7 lb. of aldehyde and $.21b. of acid. By reducing the quan tity of aldehyde fed into column 3 the percent conversion can be increased while by decreasing the percent acid drawn off from column 8, by

increasing the reflux from dephlegmator 9, the

to the higher boiling points higher temperatures would be employed.

In respect to Fig. 2, a similar type of process as already described in detail may be carried out. The oxidation would be the same. However, When operating in accordance with Fig. 2, the entire catalyst solution may be stripped principally of water, acid and some acetic anhydride and then the solution returned to the oxidation unit. Also,

- in accordance with Fig. 2 the procedure for recovering the anhydride is carried out in the adjacent still pot 51. That is, as an anhydrideacid mixture collects in 56, part thereof flows into still pot 51 where anhydride and acid in an amount substantially equivalent to that formed is distilled off through conduit 62 and condensed at 6|. A portion of the catalyst solution is circulated therethrough in accordance with Fig. 2. Or, the catalyst or catalyst solution may be circulated through a flash pot where only an amount equivalent to the increase in volume of the oxidation unit is flashed ofi to the water removal column and the rest is returned to the base of the oxidation unit as shown in Fig. 1. In another method of operation, a great quantity of liquid may be flashed off from the flash pot while the level in the oxidation unit is maintained either by returning a portion of the water-free acetic anhydride overfiowing from the base of the water removing column or by the addition of glacial acid or other liquid to the oxidation unit. By improved control of vacuum stil Seven higher anhydride yields may be obtained.-.

In the embodiments we have shown, the reduced pressure does not carry through to the oxidation unit. It will be noted that a throttling valve if provided in the connecting conduit, isolates the vacuum still from the oxidation unit as far as pressure is concerned. In the instance of oxidizing acetaldehyde by means of air or in the presence of a diluent, due to the acetic acid and anhydride havinga higher volatility than, for example, propionic acid and anhydride, that when operating around about Gil-70 C. without any flashing devices, the air mixtures passing through the unit will carry out the acetic acid and anhydride as fast as they are formed. The carried out materials may then be subjected to treatment for separatin the anhydride therefrom. 'It will also be noted that we do not have to drastically cool the anhydride acid-water catalyst mixture but that these components may be more or less treated in a heated condition or at the temperatures which they are evolved from the oxidation ste'p. Our process is preferably operated in a continuous manner as already indicated and in this respect possesses considerable advantage. By such procedure the anhydride formed is separated from detrimental components within a very short time after it is formed.

In our continuous process we are able to oxidize %-90% of the aldehyde feed in a single pass. This, of course, considerably simplifies .aldehyde separation, recovery, recirculation, etc.

- From the foregoing it is apparent that our process possesses a number of advantages over processes which have heretofore been proposed. Inasmuch as only a small amount, of the aidehyde being oxidized is in the reaction zone at any one time, and not all the aldehyde which is intended to be oxidized, there is less danger of explosion not only because of the small quantity, but also because of the fact in our process reaction products do not remain in the reaction zone for any material periods. Furthermore, our process does not require the use of pressure or cooling to=below'zero. In addition, in our process, inasmuch as the catalyst solution may be more or less substantially continuously treated to remove water and other components therefrom, our catalyst solution not only does not build up any large proportion of undesired or dangerous components, but is maintained at a constant and eflicient concentration. Consequently, in our process, by the treatment of the catalyst solution the water content is always below 10% and losses due to reaction of water and anhydride which is formed are minimized.

What we claim is;

1. In a process for the manufacture of an anhydride of an aliphatic acid having from 2-5 carbon atoms by the catalytic oxidation of the corresponding aldehyde, steps which comprise continuously introducing a small amount 01' the aldehyde into a restricted reaction zone containing a catalyst composed of a solution of an 8thgroup metal in an aliphatic acidcorresponding to the anhydride being produced, continuously w t-reducing a gaseous oxidizing medium into the .xture of aldehyde and catalyst solution, whereby a mixture containing anhydride, acid and uyater is produced, continuously withdrawing the solution containing the reaction products from the reaction zone, continuously removing anhydrlde, acid and water from the solution to the point where the water content of the solution amounts to not over about 10%, and continuously recycling the rectified solution through the reaction zone, whereby the amount of water in the reaction zone is maintained at not over about 10% of the components present therein.

2. In a process for the manufacture of an anhydride of an aliphatic acid having from 2-5 carbon atoms by the catalytic oxidation of the corresponding aldehyde, the steps which coinprise continuously introducing a small amount of the aldehyde into a restricted reaction zone containing a catalyst composed of a solution of an 8th group metal in an aliphatic acid corresponding to the anhydride being produced continuously introducing a gaseous oxidizing medium into the mixture of aldehyde and catalyst solution, whereby a mixture containing anhydride, acid and water is produced, continuously withdrawing the solution containing the reaction products from the reaction zone and thereafter continuously removing anhydride, acid and water from the solution by flash distillation under reduced pressure to the point where the water content of the-solution amounts to not over about 10%, continuously recycling the rectifled solution through the reaction zone, whereby the amount of water in the reaction zone is maintained at not over about 10% of the components present therein.

3. In a process for the manufacture of acetic anhydride by the catalytic oxidation of acetaldehyde the steps which comprise continuously introducing a small amount of the aldehyde into a restricted reaction zone containing an acetic acid solution of cobalt acetate, continuously introducing oxygen into the mixture of aldehyde i and catalyst solution, whereby a mixture of acetic anhydride, acetic acid and water is produced, continuously withdrawing the catalyst solution containing the reaction products from the reaction zone, continuously removing anhydride, acid and water from the mixture to the point where the water content of the catalyst solution amounts to not over about 10%, and continuously recycling the rectified catalyst solution through the reaction zone, whereby the amount of water in the reaction-zone is maintained at not over about 10% of the components present therein.

DAVID C. HULL, CLAIRE A. MARSHALL. 

